Free sterols, steryl esters, and lipid phosphorus in needles of scot's pine (Pinus sylvestris L.)

Abstract

AbstractFree sterols, steryl esters, and lipid phosphorus were measured in new (current year) needles of Scot's pine during an annual cycle, and also in one‐, two‐, and three‐year‐old needles collected shortly after bud break. Sterols were identified and quantified by capillary gas chromatography and gas chromatography/mass spectrometry. Steryl esters were hydrolyzed enzymatically. Newly emerged needles contained highest amounts of free sterols and lipid phosphorus, probably reflecting increased membrane and organelle production, but low levels of steryl esters. Mature needles contained approximately equal amounts of free and esterified sterols. The molar phospholipid/free sterol ratio was 3∶1 at all the time periods studied. A dramatic increase of steryl esters was observed in the one‐, two‐, and three‐year‐old needles at times when new needles emerged. The individual free and esterified sterols were sitosterol, campesterol (presumably together with its C‐24 epimer), and cholesterol, at approximately 88, 10, and 2%, respectively. Isofucosterol, an intermediate in sitosterol biosynthesis, was present almost exclusively in newly emerged needles. Esterified sterols contained only trace amounts of isofucosterol. Shifts in favor of cholesterol and 24ζ‐methyl cholesterol occurred in the steryl esters during needle differentiation, and saturation grade of esterified fatty acids decreased. In mature needles, the composition of free sterols and steryl esters remained constant throughout the year.